<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        canvas{
            border: 1px solid red;
        }
    </style>
</head>
<body>
    <canvas width="500" height="500" id="mycanvas"></canvas>


    <script>
        let canvas = document.querySelector("#mycanvas");
        // 获取上下文
        let context = canvas.getContext("2d");

        // 预加载：等待资源加载完毕之后在使用
        function loadImg(){
            return new Promise((resolve,reject)=>{
                let img = document.createElement("img");
                img.src = "https://gimg2.baidu.com/image_search/src=http%3A%2F%2Fimg.jj20.com%2Fup%2Fallimg%2Ftp02%2F1Z9191923035R0-0-lp.jpg&refer=http%3A%2F%2Fimg.jj20.com&app=2002&size=f9999,10000&q=a80&n=0&g=0n&fmt=auto?sec=1661397561&t=a620034e48d31890e7e652561c79083b";
                img.onload = function(){
                    resolve(this);
                }

                img.onerror = function(){
                    reject("图片加载失败");
                }
            })
        }
        loadImg().then(img=>{
            context.drawImage(img, 50,50,300,300);
        },err=>{
            console.log("error,err");
        })
    </script>
</body>
</html>